So I purchased a 1992 SC400 with only 36000 original miles. While this is well below the mileage required to change out the timing belt, is the number of years a factor? IOW, should the belt be changed purely because of it's chronological age?

 

My mother had a 1994Toyota Corolla with 28,000 miles on it. In 2013 I had the timing belt changed because of the age. Timing belt looked like new.
My guess would be mileage affects it more than age.